How to Clean a Roof

Over time, roofs can become dirty as a result of harsh weather, natural debris, or a build-up of moss so in order to keep yours in top working condition, you need to clean it regularly, either yourself or by hiring professionals.Moss in particular can damage roofs, so it is important to clean it off as soon as it appears in order to maintain a functional and visually-appealing roof, as well as to reduce the risk of leaks.

Safety

All work on a roof should be undertaken only with the correct safety precautions in place.

Always wear the appropriate protective clothing, particularly when working with bleach solutions, and ensure that your shoes have a sturdy grip – rubber soles are ideal.

A secure structure should be put up around the roof, and ladders should be fixed into place with someone holding to secure them at the bottom. Roof crawlers are an excellent solution for this, as they are shaped to curve over the apex of the roof, holding the ladder in place.

Pressure washing

Pressure washing is not advisable for cleaning a roof, despite the advice given by many sources. The method described below is much safer and will not have a damaging effect on your roof.

Natural debris

Falling leaves, twigs, and other natural debris can be removed very easily with either a blower or a broom. If you have the correct safety precautions in place, you can climb atop the roof and remove by hand, but, if it is possible to do so, you can remain on the ladders against the roof and remove from there.

Moss

Moss can exacerbate any potential leaks, as it can transfer moisture to the laths, causing them to become rotten and carry water down underneath the roof. Whilst some people like the visual effect of moss, it can cause long-term damage to the roof, so it is advisable to remove moss as soon as it appears.

Depending on how much moss there is on the roof, the task could become quite lengthy, as every affected tile will need to be cleaned. For this, you will need a small trowel with a pointed end and a wire brush.

Starting at the top of the roof, you will need to remove every tile individually and scrape the moss away, including along all the ridges and grooves. Sweep the brush over the tiles afterwards to remove any stubborn bits. Scrape everything into a bucket so you can correctly dispose of it. Moss can simply be thrown in a bin – there are no specific requirements for disposal.

Unless there is a leak at the very highest point in the roof, it shouldn’t be necessary to remove the top row of tiles that fit underneath the ridge tiles. Therefore, instead of cleaning every edge of these individually, give the external edge a thorough clean and scrape along all the grooves and edges to remove any moss or dirt that has gathered there.

If you need any help or advice regarding how to remove roof tiles, we have a step-by-step guide for both slate tiles and concrete/clay tiles.

As you examine each tile individually, you may notice some with broken sections in the corners or small cracks that could worsen and cause leaks. If so, take this opportunity to lay new tiles in their place in order to prevent any problems before they occur.

Tip:

Do this on a dry, clear day with little breeze, to avoid moss being swept off the roof and into your garden or driveway.

Shingle roofs

Black stains on shingle roofs can be evidence of algae building up, so it is important to tackle as soon as it occurs.

Algae grows on roofs where it can feed on the limestone that is often used in making asphalt shingles. This ultimately weakens the shingles and allows them to absorb more heat.

It is inadvisable to use a pressure washer in this instance, as this can weaken the shingles further without actually tackling the root of the algae problem. Furthermore, many manufacturers will void the warranty on your shingles if you use a pressure washer to clean them, so it is best practice to use alternative cleaning methods.

A solution of bleach and water is a more effective way of cleaning shingles. However, you must not use a chlorine-based bleach, as this can harm both the roof and any plants below or around it. Test your solution on a spare shingle to begin with, ensuring that the shingle is not damaged and that the solution is safe for use.

Spray this solution onto a small section of the roof – no more than four feet wide – and then scrub with a soft brush with a very long handle. You can either do this from a ladder fixed to the side of the roof, or by climbing onto the roof itself, ensuring that you stay on the dry sections at all times.

Tip:

Do this on an overcast, dry day rather than a sunny one, as too much sunlight could cause the solution to dry too quickly and reduce its effectiveness.

The roof should be rinsed afterwards. The solution itself could damage any nearby plant life, so if you want to protect your plants, water them thoroughly before and after rinsing the roof, as this will dilute the solution.

Cleaning a roof can reduce the risk of leaks, ensuring your roof stays looking neat and visually appealing for as long as possible. With regular maintenance, you can help your tiles last for their expected lifespan without needing replacement, and keep them and the laths beneath as healthy as possible.